Handling and towing devices are fixed to the deck of a ship. Conventionally they comprise a structure equipped with a guide device, such as a pulley, allowing the guiding of the cable and a winch allowing the cable to be hauled in and paid out. The structure is able to tilt about an axis of tilting so that the launching and recovery of the submersible object are performed by tilting the structure between an operational or towing position in which the guide device is situated in a high position and a position for launching and recovering the underwater vehicle, in which position the guide device is situated in a low position relative to the deck of the ship. Conventionally, handling devices are installed at the rear of the boat so that the guide device is situated to the rear of the tilting structure along the axis of the ship and the axis of tilting is substantially horizontal and perpendicular to the longitudinal axis of the ship.
During the phase of towing of the submersible object, the structure is rigid, which means to say that it is engineered not to deform, namely to withstand the effect of the forces associated with the sea. There are two major events that govern the specifying of the handling and towing device. A first type of event is the arrival of a high wave when the structure is in the position for launching and recovering the underwater vehicle, which applies a very high lateral force to the structure. What is meant by a lateral force is a force that has a component parallel to the axis of tilting of the structure.
A second type of event is the submersible object or the cable catching on an underwater obstacle, for example on a submarine or on the sea bed on a rock. This second type of event may bring the object along the side of the boat if the point of catching is offset laterally with respect to the axis of the ship or the axis of rotation of the structure and apply very high lateral forces to the structure as the ship moves forward.
These two types of event are exceptional but lead to lateral forces on the structure which are of the order of twice the nominal force that the structure needs to be capable of absorbing without deforming. The structure and, more generally, the handling and towing device, is therefore reinforced to withstand these exceptional forces, at the expense of the mass of the device overall.